Optical Tweezers with XYZ-Piezo Nanopositioning Stages

Investigations on interactions and forces at the level of individual molecules assist in gaining a great deal of information on chemical and mechanical properties or biological functions. Special techniques have been developed for this purpose, e.g. atomic force microscopes or so-called optical tweezers. The latter can grip, guide and manipulate miniscule objects by means of a laser beam.

Since the technique uses only the radiation pressure of the light, there is no direct contact with the sample. The main advantage of the optical tweezers over atomic force micro scopes is that observations are possible not only in the direction of the z-axis, but in all three spatial dimensions and experiments can be carried out interactively.

JPK Instruments, of Berlin, Germany has brought to market optical tweezers which provide a time-resolved detection of individual molecules and directly support many of the mathematically complex analytical methods thanks to their extensive software. The Nano-Tracker enables the user to control and manipulate particles measuring from several micrometers down to 30 nm. The corresponding samples, e.g. whole, living cells or also individual molecules, can be observed in real-time with nanometer precision.  The system allows accurate, quantifiable and reproducible measurements of a wide variety of particle or cell interactions.

The combined use of parallel kinematics and parallel direct metrology in the PIMars XYZ-stage provides the multi-axis nanopositioning system with simultaneous determination of all degrees of freedom with respect to a common fixed reference. An unintended crosstalk of the motion (e.g. as a result of an external force) into a different axis can thus be detected and actively compensated in real-time. This can keep the deviation from the trajectory down to under a few nanometers, even in dynamic operation. “The capacitive sensors integrated in the nanopositioning system make a decisive contribution to this effect. They provide direct and contact-free measurement of the position. Neither friction nor hysteresis affect the measurement, and this, combined with the position resolution of far below one nano- meter, means outstanding values for linearity can be achieved”, explains Dr. van Mameren further.